1. Field of the Invention
This invention relates to door operators for doors on transit vehicles such as buses and trains. Some vehicle doors have a single panel mounted at an outside edge of the door opening. Many vehicle doors have two panels, each mounted at an outside edge of the door opening. The panels usually swing outward to permit entrance or exit of passengers. Often, the doors are caused to open or close with a pneumatic cylinder or electric motor and a well known teeter assembly mounted over the top of the door opening. The space available for mounting the door operator over the door opening is often limited. Automatic opening and closing of the doors is controlled by the vehicle driver at stops for picking up and discharging passengers. It is an essential feature of door operators that the doors cannot be pushed open by passengers leaning against the doors, for example, while the vehicle is moving. However, in an emergency there must be a manual release that can be operated by a passenger. Generally, passengers must be able to operate the manual release with no more than 20 pounds pull force.
2. Description of Related Art
U.S. Pat. No. 5,332,279 entitled “Power Door Operator for Multi-Passenger Mass Transit Vehicles” discloses an electric door operator and illustrates the manner in which the spaced doors are rotated open and closed by the action of the teeter assembly connected to drive rods and pivot levers fixed to the vertical door shafts on which the doors are mounted. FIG. 1 of the '279 patent is incorporated herein by reference. This application is directed to an improved system for driving the teeter assembly with an electric motor.